Method and apparatus for encoding video by using transformation index, and method and apparatus for decoding video by using transformation index

ABSTRACT

Encoding and decoding a video using transformation index that indicates information that indicates a structure of a transformation unit transforming data of a current coding unit.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application is a Continuation application of U.S. patentapplication Ser. No. 13/079,983, filed on Apr. 5, 2011, in the U.S.Patent and Trademark Office, which claims the benefit of U.S.Provisional Patent Application No. 61/320,826, filed on Apr. 5, 2010, inthe U.S. Patent and Trademark Office, and priority from Korean PatentApplication No. 10-2010-0096920, filed on Oct. 5, 2010, in the KoreanIntellectual Property Office, the disclosures of which are incorporatedherein by reference in their entireties.

BACKGROUND

1. Field

The exemplary embodiments relate to video encoding and video decoding inwhich transformation between a spatial domain and a transformationdomain is performed.

2. Description of the Related Art

As hardware for reproducing and storing high resolution or high qualityvideo content is being developed and supplied, a need for a video codecfor effectively encoding or decoding the high resolution or high qualityvideo content is increasing. In a conventional video codec, a video isencoded according to a limited encoding method based on a macroblockhaving a predetermined size. In the conventional video codec, video datais encoded and decoded by performing transformation and inversetransformation on macroblocks by using blocks each having the same size.

SUMMARY

According to an aspect of an exemplary embodiment, there is provided amethod of encoding a video including: determining a transformation unitthat is a data unit in which a current coding unit is transformed, thecoding unit being a data unit in which a current picture of the video isencoded; transforming data of the current coding unit based on thedetermined transformation unit to encode the data of the current codingunit; and outputting the encoded data of the current coding unit,encoding mode information that indicates an encoding mode of the encodeddata of the current coding unit, and transformation index informationthat indicates a structure of the transformation unit transforming thedata of the current coding unit, as a bitstream.

According to another aspect of an exemplary embodiment, there isprovided a method of decoding an encoded video including: receiving abitstream of the encoded video and parsing the received bitstream;extracting encoded data of a current coding unit that is a data unit inwhich a current picture of the encoded video is encoded, encoding modeinformation that indicates an encoding mode of the encoded data of thecurrent coding unit, and transformation index information that indicatesa structure of a transformation unit that is a data unit in which thedata of the current coding unit is transformed, from the parsedbitstream; and performing inverse transformation on the encoded data ofthe current coding unit based on the transformation index information todecode the encoded data of the current coding unit transformed in thetransformation unit.

According to another aspect of an exemplary embodiment, there isprovided a video encoding apparatus including a processor, the apparatusincluding: a transformation unit determiner which determines atransformation unit that is a data unit in which a current coding unitis transformed, the coding unit being a data unit in which a currentpicture of a received video is encoded; an encoding unit whichtransforms data of the current coding unit based on the determinedtransformation unit to encode the data of the current coding unit; andan encoded data output unit which outputs the encoded data of thecurrent coding unit, encoding mode information that indicates anencoding mode of the encoded data of the current coding unit, andtransformation index information that indicates a structure of thetransformation unit transforming the data of the current coding unit.

According to another aspect of an exemplary embodiment, there isprovided a video decoding apparatus including a processor, the apparatusincluding: a receiver which receives a bitstream of an encoded video andparses the received bitstream; an extractor which extracts encoded dataof a current coding unit that is a data unit in which a current pictureof the encoded video is encoded, encoding mode information thatindicates an encoding mode of the encoded data of the current codingunit, and transformation index information that indicates a structure ofa transformation unit that is a data unit in which the current codingunit is transformed, from the parsed bitstream; and a decoder whichperforms inverse transformation on the encoded data of the currentcoding unit based on the transformation index information to decode theencoded data of the current coding unit transformed in thetransformation unit.

According to another aspect of an exemplary embodiment, there isprovided a video encoding apparatus including a processor, the apparatusincluding: a maximum coding unit splitter which splits a current pictureinto at least one maximum coding unit; a coding unit determiner whichdetermines coding units having a tree structure that include codingunits of a coded depth that are hierarchical according to depths in asame region of the at least one maximum coding unit and independent indifferent regions, by independently determining a coding unit of a codeddepth to output an encoding result for each deeper coding unit, fromamong all deeper coding units hierarchically constructed according todepths that indicate numbers of times the at least one maximum codingunit is spatially split, for each of the at least one maximum codingunit, and determining a transformation unit being a data unit in which acurrent coding unit from among the coding units having the treestructure is transformed, to encode the current coding unit by includingtransformation based on the transformation unit; and an output unitwhich encodes and outputs encoded data of the current picture,information about a coded depth of the coding units having the treestructure and an encoding mode, and transformation index informationabout a structure of transformation units of the coding units of thecoded depth, for each of the maximum coding units.

According to another aspect of an exemplary embodiment, there isprovided a video decoding apparatus including a processor, the apparatusincluding: a receiver which receives a bitstream of an encoded video andparses the received bitstream; an image data and encoded informationextractor which extracts encoded data of a picture, information about acoded depth and an encoding mode, and transformation index informationabout a structure of transformation units of the coding units of thecoded depth, according to coding units having a tree structure includedin each of a plurality of maximum coding units into which the picture issplit, from the parsed bitstream; and an image data decoder that decodesthe encoded data by performing inverse transformation on the codingunits of the coded depth, based on transformation units obtained basedon the transformation index information, for each of the plurality ofmaximum coding units, wherein the coding units having the tree structurecomprise coding units corresponding to a coded depth determined tooutput an encoding result from among deeper coding units hierarchicallyconstructed according to depths that indicate numbers of times themaximum coding unit is spatially split, when at least one of theplurality of maximum coding units is encoded.

According to another aspect of an exemplary embodiment, there isprovided a computer readable recording medium having recorded thereon aprogram for executing the method of encoding a video.

According to another aspect of an exemplary embodiment, there isprovided a computer readable recording medium having recorded thereon aprogram for executing the method of decoding a video.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and/or other aspects will become more apparent by describingin detail exemplary embodiments thereof with reference to the attacheddrawings in which:

FIG. 1 is a block diagram of a video encoding apparatus using atransformation index, according to an exemplary embodiment;

FIG. 2 is a block diagram of a video decoding apparatus using atransformation index, according to an exemplary embodiment;

FIG. 3 is a diagram illustrating the structure of a transformation unitand a transformation index, according to an exemplary embodiment;

FIG. 4 is a diagram illustrating the structure of a transformation unitand a transformation index, according to an exemplary embodiment;

FIGS. 5 and 6 are diagrams illustrating examples of use of thetransformation index according to an exemplary embodiment;

FIG. 7 is a flowchart illustrating a video encoding method using atransformation index, according to an exemplary embodiment;

FIG. 8 is a flowchart illustrating a video decoding method using atransformation index, according to an exemplary embodiment;

FIG. 9 is a block diagram of a video encoding apparatus using codingunits having a tree structure and a transformation index, according toan exemplary embodiment;

FIG. 10 is a block diagram of a video decoding apparatus using codingunits having a tree structure and a transformation index, according toan exemplary embodiment;

FIG. 11 is a diagram for describing a concept of coding units accordingto an exemplary embodiment;

FIG. 12 is a block diagram of an image encoder based on coding unitsaccording to an exemplary embodiment;

FIG. 13 is a block diagram of an image decoder based on coding unitsaccording to an exemplary embodiment;

FIG. 14 is a diagram illustrating deeper coding units according todepths, and partitions according to an exemplary embodiment;

FIG. 15 is a diagram for describing a relationship between a coding unitand transformation units, according to an exemplary embodiment;

FIG. 16 is a diagram for describing encoding information of coding unitscorresponding to a coded depth, according to an exemplary embodiment;

FIG. 17 is a diagram of deeper coding units according to depths,according to an exemplary embodiment;

FIGS. 18 through 20 are diagrams for describing a relationship betweencoding units, prediction units, and transformation units, according toan exemplary embodiment;

FIG. 21 is a diagram for describing a relationship between a codingunit, a prediction unit or partition, and a transformation unit,according to encoding mode information of Table 1;

FIG. 22 is a flowchart illustrating a video encoding method that uses atransformation index on the basis of coding units and transformationunits having a tree structure, according to an exemplary embodiment; and

FIG. 23 is a flowchart illustrating a video decoding method that use atransformation index on the basis of the coding units and thetransformation units having a tree structure, according to an exemplaryembodiment.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, the exemplary embodiments will be described more fully withreference to the accompanying drawings, in which THE exemplaryembodiments are shown. In the exemplary embodiments, “unit” may or maynot refer to a unit of size, depending on its context, and an ‘image’may denote a still image for a video or a moving image, that is, thevideo itself.

Hereinafter, a ‘coding unit’ is an encoding data unit in which the imagedata is encoded at an encoder side and an encoded data unit in which theencoded image data is decoded at a decoder side, according to exemplaryembodiments. Also, a ‘coded depth’ indicates a depth where a coding unitis encoded.

Encoding and decoding of a video by using a transformation index on thebasis of transformation units having a tree structure, according to anexemplary embodiment, will be described with reference to FIGS. 1through 8. Encoding and decoding of a video by using a transformationindex on the basis of coding units and transformation units having atree structure, according to an exemplary embodiment, be described withreference to FIGS. 9 through 23.

First, a method and apparatus for encoding video by using atransformation index and a method and apparatus for decoding video byusing a transformation index according to an exemplary embodiment willbe described with reference to FIGS. 1 to 8.

FIG. 1 is a block diagram of a video encoding apparatus 10 using atransformation index, according to an exemplary embodiment.

Referring to FIG. 1, the video encoding apparatus 10 using atransformation index includes a transformation unit determiner 12, anencoding unit 14, and an encoded data output unit 16. For convenience ofexplanation, the video encoding apparatus using a transformation indexwill be referred to as a video encoding apparatus 10. The operations ofthe transformation unit determiner 12, the encoding unit 14, and theencoded data output unit 16 of the video encoding apparatus 10 may beorganically controlled by a (not shown) video encoding processor, acentral processing unit (CPU), a graphics processing unit (GPU), or thelike.

The video encoding apparatus 10 splits a current picture of a receivedvideo into data units, each unit having a predetermined size, andperforms encoding on each of the data units, to encode the currentpicture. Hereinafter, a data unit in which the current picture isencoded is referred to as a ‘coding unit’. The video encoding apparatus10 may encode the current picture by performing predictive encodingincluding inter-prediction and intra-prediction, transformation andquantization, and entropy encoding on each coding unit.

The transformation unit determiner 12 determines a transformation unit,that is, a data unit in which a current coding unit, from among thecoding units of the current picture, is transformed. The transformationunit may be included in the current coding unit, and may be determinedto be a data unit having a size smaller than or equal to the currentcoding unit. The transformation unit determiner 12 may generate thetransformation unit by halving the height and width of the currentcoding unit, i.e., quartering the current coding unit.

The transformation unit determiner 12 may generate transformation unitsof a lower level by halving the height and width of the transformationunit. The transformation unit determiner 12 may split the current codingunit into transformation units each having the same size by splittingall transformation units into transformation units of a lower level.Since the height and width of each transformation unit are halved, thecurrent coding unit may be split into transformation units each havingthe same size, and the total number of transformation units of a lowerlevel is 4 to the power of a positive integer.

The transformation unit determiner 12 may determine transformation unitshaving a tree structure, to transform the current coding unit. Thetransformation units having a tree structure include finaltransformation units whose transformation results are determined to beoutput, from among the transformation units of the current coding unit.

In order to determine the transformation units having a tree structure,the transformation unit determiner 12 may generate transformation unitsof a lower level by repeatedly halving the height and width of atransformation unit from among the transformation units of the currentcoding unit. The transformation unit determiner 12 may determine whetherto split each transformation unit into transformation units of lowerlevel, independently from the other transformation units on the samelevel as that of the each transformation unit.

The transformation unit determiner 12 may select transformation units ofa level where a transformation error is minimized, by repeatedlytransforming transformation units of each of all levels having ahierarchical structure in the current coding unit. The transformationunit of the level allowing for a minimum transformation error may bedetermined to be a final transformation unit whose transformation resultis to be output. Accordingly, the transformation unit determiner 12 maydetermine transformation units having a tree structure according to anexemplary embodiment in which the final transformation units whosetransformation results are determined to be output are included.

The encoding unit 14 encodes the current coding unit by generatingresidual data of the current coding unit and transforming the residualdata based on the transformation units determined by the transformationunit determiner 12. ‘Transformation’ for video encoding according to anexemplary embodiment denotes a data processing technique fortransforming the data of a spatial domain of a video into the data of atransformation domain thereof. Examples of the transformation performedfor video encoding by the encoding unit 14 may include frequencytransformation, orthogonal transformation, integer transformation, andthe like.

The encoded data output unit 16 outputs encoded data of the currentcoding unit, information that indicates an encoding mode, andtransformation index information, as a bitstream.

The information about an encoding mode may include information aboutvarious methods and the like used to encode the current coding unit.

The transformation index information may be information about thestructure of a transformation unit used to transform the current codingunit. For example, the transformation index information may include thenumber of times the current coding unit is split to turn intotransformation units of a final level, and information about the sizesand shapes of the transformation units.

The transformation index information may represent whether a currenttransformation unit is split into transformation units of a lower level.For example, a transformation unit split bit corresponding to 1-bitdata, that indicates whether a current transformation unit is split intotransformation units of a lower level, may be used as the transformationindex information.

Transformation index information according to a first exemplaryembodiment may indicate whether the current transformation unit is splitinto transformation units each having the same size. For example, thetransformation index information according to the first exemplaryembodiment may indicate whether the height and width of the currentcoding unit are each halved once to obtain four transformation units orare each halved twice to obtain 16 transformation units. In other words,the transformation index information according to the first exemplaryembodiment may represent the number of 4 to the power of a positiveinteger of the transformation units each having the same size, intowhich the current coding unit is split.

Transformation index information according to a second exemplaryembodiment may indicate whether the current coding unit is split intotransformation units having various sizes according to a tree structure,according to an exemplary embodiment.

The size of a transformation unit may be determined based on thetransformation index and a prediction unit type or a partition type of acurrent coding unit. For example, the size of a transformation unitcorresponding to the transformation index may vary according to aprediction unit type or a partition type of a coding unit.

If the current transformation unit is split into transformation unitseach having the same size, the current size of the transformation unitmay be determined based on the transformation index and a predictionunit type or a partition type of a corresponding coding unit. Also, if acurrent coding unit is split into transformation units having varioussizes according to a tree structure, the size of a currenttransformation unit may be determined based on the transformation indexand a prediction unit type or a partition type of the current codingunit.

According to an exemplary embodiment, the maximum size of atransformation unit may be equal to the size of a current coding unit.According to other exemplary embodiment, the maximum size of atransformation unit may be determined base on a prediction unit type ora partition type of a current prediction unit or partition. For example,the maximum size of the current transformation unit size may indicatethe size of a maximum square included in the current prediction unit orpartition.

For example, the transformation index information according to thesecond exemplary embodiment may be represented as a bitstring obtainedby arranging transformation unit split bits of transformation units ofrespective levels that are obtained until the current coding unit issplit into transformation units having the tree structure. Thetransformation index information according to the second exemplaryembodiment may include a bitstring obtained by arranging transformationunit split bits of adjacent transformation units of the same level in asequence where the transformation units are scanned in a zigzag manner.When a predetermined transformation unit may be split intotransformation units of a lower level having a hierarchical structure,the transformation index information according to the second exemplaryembodiment may include a bitstring obtained by arranging transformationunit split bits of the transformation units of the lower level in asequence where the transformation units are scanned in a zigzag manner.

FIG. 2 is a block diagram of a video decoding apparatus using atransformation index, according to an exemplary embodiment

Referring to FIG. 2, the video decoding apparatus 20 using atransformation index includes a receiver 22, an extractor 24, and adecoder 26. For convenience of explanation, the video decoding apparatus20 using a transformation index will be referred to as a video decodingapparatus 20. The operations of the receiver 22, the extractor 24, andthe decoder 26 of the video decoding apparatus 20 may be controlled by a(not shown) video decoding processor, a CPU, a GPU, or the like.

To decode a current picture of a received video, the video decodingapparatus 20 may decode the current picture by performing entropydecoding, dequantization, inverse transformation, and predictivedecoding, including inter-prediction/compensation andintra-prediction/compensation, on each coding unit of the currentpicture.

The receiver 22 receives and parses a bitstream for an encoded video.The extractor 24 extracts encoded data of each coding unit of thecurrent picture, information about an encoding mode, and transformationindex information of a current coding unit, from the bitstream parsed bythe receiver 22.

The decoder 26 decodes the encoded data by generating transformationunits of the current coding unit according to the transformation indexinformation extracted by the extractor 24 and performing inversetransformation on the current coding unit on the basis of thetransformation units. As a result of the decoding of coding units, thecurrent picture may be restored.

The concept of the transformation unit is similar to that describedabove with reference to the video encoding apparatus 10 of FIG. 1. Inother words, a transformation unit according to an exemplary embodimentmay be a transformation unit obtained by halving the height and width ofthe current coding unit or a transformation unit of an upper level. Allof the transformation units included in the current coding unitaccording to an exemplary embodiment may have the same size. Atransformation unit according to another exemplary embodiment is atransformation unit of one level from among the transformation units ofthe current coding unit that have a tree structure, and may be splitinto transformation units of a lower level through repetitive splittingfor each level of transformation unit or into transformation units of alower level through independent splitting between adjacenttransformation units.

The decoder 26 may read information that indicates the number of timesthe current coding unit is split to turn into transformation units of afinal level, information about the sizes and shapes of thetransformation units, and the like, from the transformation indexinformation.

The decoder 26 may read information that indicates whether a currenttransformation unit is split into transformation units of a lower level,from the transformation index information.

The decoder 26 may read information that indicates the level of atransformation unit from a transformation index according to a firstexemplary embodiment. In this case, since the current coding unit issplit into transformation units of the same sizes for each level untiltransformation units of a final level are obtained, the decoder 26 maydetermine the transformation units of the final level having the samesize by determining the final level of transformation units according tothe transformation index and halving the heights and widths of all ofthe transformation units of an upper level when the current coding unitis split into the transformation units of the final level.

The decoder 26 may determine the size of a transformation unit based onthe transformation index and a prediction unit type or a partition typeof a current coding unit. For example, the size of a transformation unitcorresponding to the transformation index may vary according to aprediction unit type or a partition type of a coding unit.

If the decoder 26 may split a current coding unit and then determine thecurrent transformation units having the same size, the size of thecurrent transformation unit may be determined based on thetransformation index and a prediction unit type or a partition type ofthe current coding unit. Also, if a current coding unit is split intotransformation units having various sizes according to a tree structure,a size of a current transformation unit may be determined based on thetransformation index and a prediction unit type or a partition type ofthe current coding unit.

The decoder 26 may determine transformation units obtained according toa tree structure, based on transformation index information according toa second exemplary embodiment. For example, a bitstring of thetransformation index information according to the second exemplaryembodiment may be a bitstring obtained by arranging transformation unitsplit bits for transformation units of each level. The decoder 26 maydetermine transformation units into which the current coding unit issplit according to a tree structure, by reading the bitstring of thetransformation index information according to the second exemplaryembodiment and splitting the current coding unit so that independentsplitting is performed between transformation units on the same leveland that repetitive splitting is performed between levels.

At this time, the decoder 26 may read transformation unit split bits ofthe transformation units on the same level from the transformation indexinformation according to the second exemplary embodiment and may splittransformation units on an upper level into transformation units on alower level in a zigzag scan sequence. When a transformation unit of anupper level is split into transformation units of a lower level, thedecoder 26 may read the transformation unit split bits of thetransformation units of the lower level, which are included in thetransformation unit of the upper level, in a zigzag scan sequence.

The inverse transformation performed for video decoding by the decoder26 may be referred to as a process of transforming data of atransformation domain into data of a spatial domain. Examples of theinverse transformation performed by the decoder 26 may include frequencyinverse-transformation, orthogonal inverse-transformation, integerinverse-transformation, and the like.

The video encoding apparatus 10 and the video decoding apparatus 20 mayefficiently encode and decode information used to determine varioussizes and shapes of transformation units having a tree structure, whichare necessary for performing transformation and inverse transformationduring video encoding and decoding based on various sizes and shapes ofcoding units, by using the transformation index according to anexemplary embodiment.

FIG. 3 is a diagram illustrating the structure of a transformation unitand a transformation index, according to a first exemplary embodiment.

A transformation unit group 32 of level 0, a transformation unit group34 of level 1, and a transformation unit group 36 of level 2 areillustrated according to a transformation index, as the transformationunit structure according to the first embodiment that includestransformation units of the same sizes in order to transform a codingunit CU0 30. The transformation index according to the first exemplaryembodiment may represent the number of times the coding unit CU0 30 issplit to turn into a transformation unit group of a current level, thatis, a level number.

In other words, the transformation unit group 32 of level 0 includes atransformation unit TU0 that has the same size as the coding unit CUO 30by splitting the height and width of the coding unit CUO 30 zero times.In this case, the transformation index of the transformation unit group32 of level 0 is 0.

The transformation unit group 34 of level 1 includes transformationunits TU10, TU11, TU12, and TU13 each having a height and a width beinghalf of those of the coding unit CUO 30, by splitting the height andwidth of the coding unit CUO 30 once. In this case, the transformationindex of the transformation unit group 34 of level 1 is 1.

The transformation unit group 36 of level 2 includes transformationunits TU20, TU21, TU22, TU23, TU24, TU25, TU26, TU27, TU28, TU29, TU2A,TU2B, TU2C, TU2D, TU2E, and TU2F each having a height and size being aquarter of those of the coding unit CUO 30, by splitting the height andwidth of the coding unit CUO 30 twice. In this case, the transformationindex of the transformation unit group 36 of level 2 is 2.

FIG. 4 is a diagram illustrating the structure of a transformation unitand a transformation index, according to a second exemplary embodiment.

A transformation unit group 40 is illustrated as the transformation unitstructure according to the second exemplary embodiment that includestransformation units having a tree structure in order to transform thecoding unit CU0 30. The transformation index according to the secondexemplary embodiment may be represented as a bitstring of transformationunit split bits for each level that is used until the transformationunits having a tree structure are obtained from the coding unit CU0 30.

In other words, since a transformation unit of level 0 having the samesize as the coding unit CU0 30 is divided into transformation unitsTU40, TU41, TU42, and TU43 of level 1, a transformation unit split bit 1for level 1 may be generated and included in the transformation index.Since transformation unit split bits for transformation units on thesame level are arranged in a zigzag scanning sequence, transformationunit split bits for level 0 may be arranged in a sequence oftransformation unit split bits for the transformation units TU40, TU41,TU42, and TU43. Since the transformation units TU40 and TU41 are notsplit, transformation unit split bits 0 and 0 for the transformationunits TU40 and TU41 may be sequentially generated and included in thetransformation index.

The transformation unit TU42 of level 1 is further split intotransformation units TU50, TU51, TU52, and TU53 of level 2. Accordingly,a transformation unit split bit 1 for the transformation unit TU42 oflevel 1 may be generated. When a transformation unit of a current levelis split into transformation units of a lower level, transformation unitsplit bits for the transformation units of the lower level may beincluded in the transformation index. Accordingly, a transformation unitsplit bit 0 for the transformation unit TU50 of level 2, atransformation unit split bit 1 for the transformation unit TU51 oflevel 2, a transformation unit split bit 0 for the transformation unitTU52 of level 2, and a transformation unit split bit 0 for thetransformation unit TU53 of level 2 may be sequentially included in thetransformation index. The transformation unit TU51 of level 2 is furthersplit into transformation units TU60, TU61, TU62, and TU63 of level 3. Atransformation unit of level 3 is a minimum transformation unit or aminimum unit, and the transformation unit of level 3 is not furthersplit.

In other words, if a transformation unit split bit for a transformationunit of a current level is 1 and transformation units of a lower levelare not the minimum transformation unit or the minimum unit,transformation unit split bits for the transformation units of the lowerlevel may be consecutively arranged after the transformation unit splitbit for the transformation unit of the current level.

Lastly, since the transformation unit TU43 of level 1 is not split, thetransformation unit split bit 0 may be included in the transformationindex.

Accordingly, the transformation index according to the second exemplaryembodiment for the coding unit CUO 30 may be determined to be 1, 0, 0,1, 0, 1, 0, 0, 0. If transformation unit split bits for transformationunits of a lower level are consecutively 0, it may be understood thatthe transformation units of the lower level are not further split.

The transformation unit split bits generated in this way are arranged,starting from the transformation unit of level 0 having the same size asthe coding unit, in such a way that transformation unit split bits oftransformation units on the same level are arranged in a zigzag scanningsequence and that if a transformation unit of a predetermined level issplit into transformation units of a lower level having a hierarchicalstructure, transformation unit split bits for the transformation unitsof the lower level are arranged in a zigzag scanning sequence, wherebythe transformation index according to the second exemplary embodimentmay be determined.

FIGS. 5 and 6 are diagrams illustrating examples of use of thetransformation index according to the second exemplary embodiment.

As described above with reference to FIG. 4, if a transformation unit isnot further split, transformation unit split bits are not furthergenerated. Thus, the transformation index according to the secondexemplary embodiment may be set according to the size of the minimumtransformation unit or the minimum unit.

When a minimum transformation unit 52 of a coding unit 50 of a 2N×2Nsize has a size of N×N, the coding unit 50 may be only split until N×Ntransformation units are obtained, and thus a transformation index ofthe coding unit 50 for a transformation unit group 54 may be set to be1.

On the other hand, when a minimum transformation unit 62 of a codingunit 60 of a 2N×2N size has a size of (N/2)×(N/2), transformation unitsof a N×N size in a transformation unit group 64 may be each split onemore time. Accordingly, a transformation index of the coding unit 60 forthe transformation unit group 64 may include, not only a transformationunit split bit 1 for a transformation unit of level 0, but alsotransformation unit split bits 0, 0, 0, and 0 for the transformationunits of level 1 in the transformation unit group 64.

The transformation units described above with reference to FIGS. 3through 6 may be determined by the transformation unit determiner 12 ofthe video encoding apparatus 10, and the transformation index may beencoded by the encoded data output unit 14. The extractor 24 of thevideo decoding apparatus 20 may extract transformation indexinformation, and the decoder 26 thereof may form a transformation unitby reading the transformation index, and perform inverse transformationon the transformation unit.

FIG. 7 is a flowchart illustrating a video encoding method using atransformation index, according to an exemplary embodiment.

In operation 72, a transformation unit, that is, a data unit in which acurrent coding unit from among coding units of a current picture istransformed, is determined. The transformation unit may be determined tobe a data unit having a size smaller than or equal to the current codingunit so that the transformation unit is included in the current codingunit, and the transformation unit may be generated by halving the heightand width of the coding unit. Since the transformation unit may form ahierarchical structure, transformation units of a lower level may begenerated by halving the height and width of a transformation unit of anupper level. For example, all transformation units of a predeterminedlevel within a current coding unit may be split into transformationunits of a lower level, so that as many transformation units of the samesize as the number of 4 to the power of a positive integer may begenerated.

The transformation unit may include final transformation units whosetransformation results are determined to be output, from among thetransformation units of the current coding unit.

The hierarchical structure of transformation units according to anexemplary embodiment may be a tree structure. While the height and widthof a current transformation unit from among the transformation units ofthe current coding unit are repeatedly halved, it is determined whetherthe halving is performed independently from the other transformationunits, and thus transformation units of a lower level are generated. Thetransformation units on each level within the same region may form ahierarchical structure. Final transformation units are determined fromamong the transformation units generated in this way so thattransformation results are output, so that transformation units having atree structure according to an exemplary embodiment may be obtained.

Transformation units of a level where an error, due to transformationfor each transformation unit, is minimized may be selected as the finaltransformation units whose transformation results are output, byrepeatedly performing transformation on each level for transformationunits having a hierarchical structure in the current coding unit andcomparing the results of the transformations with each other.

In operation 74, the current coding unit is encoded, includingtransformation based on the transformation unit. In operation 76,encoded data of the current coding unit, information about an encodingmode, and transformation index information are output.

The transformation index information about the structure of atransformation unit according to an exemplary embodiment may indicatewhether a current transformation unit is split into transformation unitsof a lower level. The transformation index information about thestructure of a transformation unit according to an exemplary embodimentmay include the number of times the current coding unit is split to turninto transformation units of a final level, and information about thesizes and shapes of the transformation units.

Transformation index information according to a first exemplaryembodiment may indicate a level that identifies the total number ofsplitting times from a current coding unit to a coding unit of a finallevel. The transformation units of each level may have the same sizes.

Transformation index information according to a second exemplaryembodiment may indicate whether the current coding unit is repeatedlysplit to obtain transformation units having a tree structure. Thetransformation index information according to the second exemplaryembodiment may be in the shape of a bitstring obtained by arrangingtransformation unit split bits that indicate whether a transformationunit of each level is split into transformation units of a lower level.The bitstring of the transformation index information may be obtained byarranging transformation unit split bits of adjacent transformationunits of the same level in a sequence where the transformation units arescanned in a zigzag manner. When a current transformation unit includestransformation units of a lower level having a hierarchical structure, abitstring of the transformation index information may be determined sothat transformation unit split bits of the transformation units of alower level are arranged in a sequence where the transformation unitsare scanned in a zigzag manner.

FIG. 8 is a flowchart illustrating a video decoding method using atransformation index, according to an exemplary embodiment.

In operation 82, a bitstream for an encoded video is received andparsed.

In operation 84, encoded data of a current coding unit of a currentpicture, information about an encoding mode, and transformation indexinformation are extracted from the parsed bitstream.

In operation 86, inverse transformation is performed on the currentcoding unit, based on transformation units obtained according to thetransformation index information, and thus the encoded data is decoded.As a result of the decoding of each coding unit, the current picture maybe restored. Whether a current transformation unit is split intotransformation units of a lower level may be read based on thetransformation index information about the structure of a transformationunit according to an exemplary embodiment, and the transformation unitsmay be determined. The inverse transformation on the current coding unitmay be performed based on the transformation units.

The number of times the current coding unit is split untiltransformation units of a final level is obtained, and information aboutthe sizes, shapes, and the like, of the transformation units may be readfrom the transformation index information about the structure of atransformation unit according to an exemplary embodiment.

A level that indicates the total number of splitting times from thecurrent coding unit to a transformation unit of a final level may beread from the transformation index information according to the firstexemplary embodiment. The level of a transformation unit indicates thenumber of times the current coding unit is split to obtain 4transformation units each having the same size. Accordingly, a structureof transformation units in which the current coding unit is split intotransformation units each having the same size may be determined.

A bitstring of transformation unit split bits that indicates whether atransformation unit of each level is split into transformation units ofa lower level is read from the transformation index informationaccording to the second exemplary embodiment, until the current codingunit is repeatedly split to obtain transformation units having the treestructure. Thus, a structure of transformation units into which thecurrent coding unit is split according to the tree structure may bedetermined

For example, transformation unit split bits of adjacent transformationunits on the same level, from among the transformation index informationaccording to the second exemplary embodiment, may be read in a sequencewhere the transformation units are scanned in a zigzag manner. Moreover,transformation unit split bits of transformation units of a lower levelhaving a hierarchical structure included in a transformation unit of apredetermined level, from among transformation index informationaccording to another exemplary embodiment, may be read in a sequencewhere the transformation units of the lower level are scanned in azigzag manner.

First, a method and apparatus for encoding video by using a coding unithaving a tree structure and a transformation index, and a method andapparatus for decoding video by using a coding unit having a treestructure and a transformation index, according to an exemplaryembodiment will be described with reference to FIGS. 9 to 23.

FIG. 9 is a block diagram of a video encoding apparatus 100, which usesa transformation index on the basis of coding units and transformationunits having a tree structure, according to an exemplary embodiment.

The video encoding apparatus 100, which uses the transformation indexbased on coding units and transmission units having a tree structure,includes a maximum coding unit splitter 110, a coding unit determiner120, and an output unit 130. For convenience of explanation, the videoencoding apparatus 100, which uses the transformation index based oncoding units and transmission units having a tree structure, is referredto as a video encoding apparatus 100.

The maximum coding unit splitter 110 may split a current picture basedon a maximum coding unit for the current picture of an image. If thecurrent picture is larger than the maximum coding unit, image data ofthe current picture may be split into the at least one maximum codingunit. The maximum coding unit according to an exemplary embodiment maybe a data unit having a size of 32×32, 64×64, 128×128, 256×256, etc.,wherein a shape of the data unit is a square having a width and heightin squares of 2. The image data may be output to the coding unitdeterminer 120 according to the at least one maximum coding unit.

A coding unit according to an exemplary embodiment may be characterizedby a maximum size and a depth. The depth denotes a number of times thecoding unit is spatially split from the maximum coding unit, and as thedepth deepens or increases, deeper encoding units according to depthsmay be split from the maximum coding unit to a minimum coding unit. Adepth of the maximum coding unit is an uppermost depth and a depth ofthe minimum coding unit is a lowermost depth. Since a size of a codingunit corresponding to each depth decreases as the depth of the maximumcoding unit deepens, a coding unit corresponding to an upper depth mayinclude a plurality of coding units corresponding to lower depths.

As described above, the image data of the current picture is split intothe maximum coding units according to a maximum size of the coding unit,and each of the maximum coding units may include deeper coding unitsthat are split according to depths. Since the maximum coding unitaccording to an exemplary embodiment is split according to depths, theimage data of a spatial domain included in the maximum coding unit maybe hierarchically classified according to depths.

A maximum depth and a maximum size of a coding unit, which limit thetotal number of times a height and a width of the maximum coding unitare hierarchically split may be predetermined.

The coding unit determiner 120 encodes at least one split regionobtained by splitting a region of the maximum coding unit according todepths, and determines a depth to output a finally encoded image dataaccording to the at least one split region. In other words, the codingunit determiner 120 determines a coded depth by encoding the image datain the deeper coding units according to depths, according to the maximumcoding unit of the current picture, and selecting a depth having theleast encoding error. Thus, the encoded image data of the coding unitcorresponding to the determined coded depth is finally output. Also, thecoding units corresponding to the coded depth may be regarded as encodedcoding units.

The determined coded depth and the encoded image data according to thedetermined coded depth are output to the output unit 130.

The image data in the maximum coding unit is encoded based on the deepercoding units corresponding to at least one depth equal to or below themaximum depth, and results of encoding the image data are compared basedon each of the deeper coding units. A depth having the least encodingerror may be selected after comparing encoding errors of the deepercoding units. At least one coded depth may be selected for each maximumcoding unit.

The size of the maximum coding unit is split as a coding unit ishierarchically split according to depths, and as the number of codingunits increases. Also, even if coding units correspond to same depth inone maximum coding unit, it is determined whether to split each of thecoding units corresponding to the same depth to a lower depth bymeasuring an encoding error of the image data of the each coding unit,separately. Accordingly, even when image data is included in one maximumcoding unit, the image data is split to regions according to the depthsand the encoding errors may differ according to regions in the onemaximum coding unit, and thus the coded depths may differ according toregions in the image data. Thus, one or more coded depths may bedetermined in one maximum coding unit, and the image data of the maximumcoding unit may be divided according to coding units of at least onecoded depth.

Accordingly, the coding unit determiner 120 may determine coding unitshaving a tree structure included in the maximum coding unit. The ‘codingunits having a tree structure’ according to an exemplary embodimentinclude coding units corresponding to a depth determined to be the codeddepth, from among all deeper coding units included in the maximum codingunit. A coding unit of a coded depth may be hierarchically determinedaccording to depths in the same region of the maximum coding unit, andmay be independently determined in different regions. Similarly, a codeddepth in a current region may be independently determined from a codeddepth in another region.

A maximum depth according to an exemplary embodiment is an index relatedto the number of splitting times from a maximum coding unit to a minimumcoding unit. A first maximum depth according to an exemplary embodimentmay denote the total number of splits from the maximum coding unit tothe minimum coding unit. A second maximum depth according to anexemplary embodiment may denote the total number of depth levels fromthe maximum coding unit to the minimum coding unit. For example, when adepth of the maximum coding unit is 0, a depth of a coding unit, inwhich the maximum coding unit is split once, may be set to 1, and adepth of a coding unit, in which the maximum coding unit is split twice,may be set to 2. Here, if the minimum coding unit is a coding unit inwhich the maximum coding unit is split four times, 5 depth levels ofdepths 0, 1, 2, 3 and 4 exist, and thus the first maximum depth may beset to 4, and the second maximum depth may be set to 5.

Prediction encoding and transformation may be performed according to themaximum coding unit. The prediction encoding and the transformation arealso performed based on the deeper coding units according to a depthequal to or depths less than the maximum depth, according to the maximumcoding unit. Transformation may be performed according to method oforthogonal transformation or integer transformation.

Since the number of deeper coding units increases whenever the maximumcoding unit is split according to depths, encoding including theprediction encoding and the transformation is performed on all of thedeeper coding units generated as the depth deepens. For convenience ofdescription, the prediction encoding and the transformation will now bedescribed based on a coding unit of a current depth, in a maximum codingunit.

The video encoding apparatus 100 may variably select a size or shape ofa data unit for encoding the image data. In order to encode the imagedata, operations, such as prediction encoding, transformation, andentropy encoding, are performed, and at this time, the same data unitmay be used for all operations or different data units may be used foreach operation.

For example, the video encoding apparatus 100 may select not only acoding unit for encoding the image data, but also a data unit differentfrom the coding unit to perform the prediction encoding on the imagedata in the coding unit.

In order to perform prediction encoding in the maximum coding unit, theprediction encoding may be performed based on a coding unitcorresponding to a coded depth, i.e., based on a coding unit that is nolonger split to coding units corresponding to a lower depth.Hereinafter, the coding unit that is no longer split and becomes a basisunit for prediction encoding will be referred to as a ‘prediction unit’.A partition obtained by splitting the prediction unit may include aprediction unit or a data unit obtained by splitting at least one of aheight and a width of the prediction unit.

For example, when a coding unit of 2N×2N (where N is a positive integer)is no longer split and becomes a prediction unit of 2N×2N, and a size ofa partition may be 2N×2N, 2N×N, N×2N, or N×N. Examples of a partitiontype include symmetrical partitions that are obtained by symmetricallysplitting a height or width of the prediction unit, partitions obtainedby asymmetrically splitting the height or width of the prediction unit,such as 1:n or n:1, partitions that are obtained by geometricallysplitting the prediction unit, and partitions having arbitrary shapes.

A prediction mode of the prediction unit may be at least one of an intramode, a inter mode, and a skip mode. For example, the intra mode or theinter mode may be performed on the partition of 2N×2N, 2N×N, N×2N, orN×N. Also, the skip mode may be performed only on the partition of2N×2N. The encoding is independently performed on one prediction unit ina coding unit, thereby selecting a prediction mode having a leastencoding error.

The video encoding apparatus 100 may also perform the transformation onthe image data in a coding unit based not only on the coding unit forencoding the image data, but also based on a data unit that is differentfrom the coding unit.

As described above with reference to FIGS. 1 through 8, in order toperform the transformation in the coding unit, the transformation may beperformed based on a data unit having a size smaller than or equal tothe coding unit. For example, the data unit for the transformation mayinclude a data unit for an intra mode and a data unit for an inter mode.

A data unit used as a base of the transformation will be referred to asa ‘transformation unit’. A transformation depth that indicates thenumber of splits to reach the transformation unit by splitting theheight and width of the coding unit may also be set in thetransformation unit. For example, in a current coding unit of 2N×2N, atransformation depth may be 0 when the size of a transformation unit isalso 2N×2N, may be 1 when each of the height and width of the currentcoding unit is split into two equal parts, totally split into 4¹transformation units, and the size of the transformation unit is thusN×N, and may be 2 when each of the height and width of the currentcoding unit is split into four equal parts, totally split into 4²transformation units and the size of the transformation unit is thusN/2×N/2. For example, the transformation unit may be set according to ahierarchical tree structure, in which a transformation unit of an uppertransformation depth is split into four transformation units of a lowertransformation depth according to the hierarchical characteristics of atransformation depth.

Similar to the coding unit, the transformation unit in the coding unitmay be recursively split into smaller sized regions, so that thetransformation unit may be determined independently in units of regions.Thus, residual data in the coding unit may be divided according to thetransformation having the tree structure according to transformationdepths.

Encoding information according to coding units corresponding to a codeddepth requires not only information about the coded depth, but alsoabout information related to prediction encoding and transformation.Accordingly, the coding unit determiner 120 not only determines a codeddepth having a least encoding error, but also determines a partitiontype in a prediction unit, a prediction mode according to predictionunits, and a size of a transformation unit for transformation.

Coding units according to a tree structure in a maximum coding unit anda method of determining a partition, according to exemplary embodiments,will be described in detail later with reference to FIGS. 11 and 12.

The coding unit determiner 120 may measure an encoding error of deepercoding units according to depths by using Rate-Distortion Optimizationbased on Lagrangian multipliers.

The output unit 130 outputs the image data of the maximum coding unit,which is encoded based on the at least one coded depth determined by thecoding unit determiner 120, and information about the encoding modeaccording to the coded depth, in bitstreams.

The encoded image data may be obtained by encoding residual data of animage.

The information about the encoding mode according to coded depth mayinclude information about the coded depth, about the partition type inthe prediction unit, the prediction mode, and the size of thetransformation unit.

The information about the coded depth may be defined by using splitinformation according to depths, which indicates whether encoding isperformed on coding units of a lower depth instead of a current depth.If the current depth of the current coding unit is the coded depth,image data in the current coding unit is encoded and output, and thusthe split information may be defined not to split the current codingunit to a lower depth. Alternatively, if the current depth of thecurrent coding unit is not the coded depth, the encoding is performed onthe coding unit of the lower depth, and thus the split information maybe defined to split the current coding unit to obtain the coding unitsof the lower depth.

If the current depth is not the coded depth, encoding is performed onthe coding unit that is split into the coding unit of the lower depth.Since at least one coding unit of the lower depth exists in one codingunit of the current depth, the encoding is repeatedly performed on eachcoding unit of the lower depth, and thus the encoding may be recursivelyperformed for the coding units having the same depth.

Since the coding units having a tree structure are determined for onemaximum coding unit, and information about at least one encoding mode isdetermined for a coding unit of a coded depth, information about atleast one encoding mode may be determined for one maximum coding unit.Also, a coded depth of the image data of the maximum coding unit may bedifferent according to locations since the image data is hierarchicallysplit according to depths, and thus information about the coded depthand the encoding mode may be set for the image data.

Accordingly, the output unit 130 may assign encoding information about acorresponding coded depth and an encoding mode to at least one of thecoding unit, the prediction unit, and a minimum unit included in themaximum coding unit.

The minimum unit according to an exemplary embodiment is a rectangulardata unit obtained by splitting the minimum coding unit constituting thelowermost depth by 4. Alternatively, the minimum unit may be a maximumrectangular data unit that may be included in all of the coding units,prediction units, partition units, and transformation units included inthe maximum coding unit.

For example, the encoding information output through the output unit 130may be classified into encoding information according to coding units,and encoding information according to prediction units. The encodinginformation according to the coding units may include the informationabout the prediction mode and about the size of the partitions. Theencoding information according to the prediction units may includeinformation about an estimated direction of an inter mode, about areference image index of the inter mode, about a motion vector, about achroma component of an intra mode, and about an interpolation method ofthe intra mode. Also, information about a maximum size of the codingunit defined according to pictures, slices, or GOPs, and informationabout a maximum depth may be inserted into SPS (Sequence Parameter Set)or a header of a bitstream. Furthermore, the encoding information outputthrough the output unit 130 may include transformation index informationabout a structure of a transformation unit according to an exemplaryembodiment, as described above with reference to FIGS. 1 through 8.

In the video encoding apparatus 100, the deeper coding unit may be acoding unit obtained by dividing a height or width of a coding unit ofan upper depth, which is one layer above, by two. In other words, whenthe size of the coding unit of the current depth is 2N×2N, the size ofthe coding unit of the lower depth is N×N. Also, the coding unit of thecurrent depth having the size of 2N×2N may include a maximum of 4 codingunits of the lower depth.

Accordingly, the video encoding apparatus 100 may form the coding unitshaving the tree structure by determining coding units having an optimumshape and an optimum size for each maximum coding unit, based on thesize of the maximum coding unit and the maximum depth determinedconsidering characteristics of the current picture. Also, since encodingmay be performed on each maximum coding unit by using any one of variousprediction modes and transformations, an optimum encoding mode may bedetermined considering characteristics of the coding unit of variousimage sizes.

Thus, if an image having high resolution or large data amount is encodedin a conventional macroblock, a number of macroblocks per pictureexcessively increases. Accordingly, a number of pieces of compressedinformation generated for each macroblock increases, and thus it isdifficult to transmit the compressed information and data compressionefficiency decreases. However, by using the video encoding apparatus100, image compression efficiency may be increased since a coding unitis adjusted while considering characteristics of an image whileincreasing a maximum size of a coding unit while considering a size ofthe image.

FIG. 10 is a block diagram of a video decoding apparatus 200 usingcoding units having a tree structure and a transformation index,according to an exemplary embodiment.

The video decoding apparatus 200 includes a receiver 210, an image dataand encoding information extractor 220, and an image data decoder 230.Various terms, such as a coding unit, a depth, a prediction unit, atransformation unit, and information about various encoding modes, forvarious operations of the video decoding apparatus 200 are identical tothose described with reference to FIG. 9 and the video encodingapparatus 100.

The receiver 210 receives and parses a bitstream of an encoded video.The image data and encoding information extractor 220 extracts encodedimage data for each coding unit from the parsed bitstream, wherein thecoding units have a tree structure according to each maximum codingunit, and outputs the extracted image data to the image data decoder230. The image data and encoding information extractor 220 may extractinformation about a maximum size of a coding unit of a current picture,from a header about the current picture or SPS.

Also, the image data and encoding information extractor 220 extractsinformation about a coded depth and an encoding mode for the codingunits having a tree structure according to each maximum coding unit,from the parsed bitstream. The extracted information about the codeddepth and the encoding mode is output to the image data decoder 230. Inother words, the image data in a bit stream is split into the maximumcoding unit so that the image data decoder 230 decodes the image datafor each maximum coding unit.

The information about the coded depth and the encoding mode according tothe maximum coding unit may be set for information about at least onecoding unit corresponding to the coded depth, and information about anencoding mode may include information about a partition type of acorresponding coding unit corresponding to the coded depth, about aprediction mode, and a size of a transformation unit. Also, splittinginformation according to depths may be extracted as the informationabout the coded depth. Furthermore, the image data and encodinginformation extractor 220 may extract transformation index informationabout a structure of a transformation unit according to an embodiment asdescribed above with reference to FIGS. 1 through 8 as the extractedinformation about the coded depth and the encoding mode.

The information about the coded depth and the encoding mode according toeach maximum coding unit extracted by the image data and encodinginformation extractor 220 is information about a coded depth and anencoding mode determined to generate a minimum encoding error when anencoder, such as the video encoding apparatus 100, repeatedly performsencoding for each deeper coding unit according to depths according toeach maximum coding unit. Accordingly, the video decoding apparatus 200may restore an image by decoding the image data according to a codeddepth and an encoding mode that generates the minimum encoding error.

Since encoding information about the coded depth and the encoding modemay be assigned to a predetermined data unit from among a correspondingcoding unit, a prediction unit, and a minimum unit, the image data andencoding information extractor 220 may extract the information about thecoded depth and the encoding mode according to the predetermined dataunits. The predetermined data units to which the same information aboutthe coded depth and the encoding mode is assigned may be inferred to bethe data units included in the same maximum coding unit.

The image data decoder 230 restores the current picture by decoding theimage data in each maximum coding unit based on the information aboutthe coded depth and the encoding mode according to the maximum codingunits. In other words, the image data decoder 230 may decode the encodedimage data based on the extracted information about the partition type,the prediction mode, and the transformation unit for each coding unitfrom among the coding units having the tree structure included in eachmaximum coding unit. A decoding process may include a predictionincluding intra prediction and motion compensation, and an inversetransformation. Inverse transformation may be performed according tomethod of inverse orthogonal transformation or inverse integertransformation.

The image data decoder 230 may perform intra prediction or motioncompensation according to a partition and a prediction mode of eachcoding unit, based on the information about the partition type and theprediction mode of the prediction unit of the coding unit according tocoded depths.

Also, the image data decoder 230 may perform inverse transformationaccording to each transformation unit in the coding unit, based on theinformation about the size of the transformation unit of the coding unitaccording to coded depths, to perform the inverse transformationaccording to maximum coding units.

The image data decoder 230 may determine at least one coded depth of acurrent maximum coding unit by using split information according todepths. If the split information indicates that image data is no longersplit in the current depth, the current depth is a coded depth.Accordingly, the image data decoder 230 may decode encoded data of atleast one coding unit corresponding to the each coded depth in thecurrent maximum coding unit by using the information about the partitiontype of the prediction unit, the prediction mode, and the size of thetransformation unit for each coding unit corresponding to the codeddepth, and output the image data of the current maximum coding unit.

In other words, data units containing the encoding information thatindicates the same split information may be gathered by observing theencoding information set assigned for the predetermined data unit fromamong the coding unit, the prediction unit, and the minimum unit, andthe gathered data units may be considered to be one data unit to bedecoded by the image data decoder 230 in the same encoding mode.

The video decoding apparatus 200 may obtain information about at leastone coding unit that generates the minimum encoding error when encodingis recursively performed for each maximum coding unit, and may use theinformation to decode the current picture. In other words, the codingunits having the tree structure determined to be the optimum codingunits in each maximum coding unit may be decoded. Also, the maximum sizeof coding unit is determined considering resolution and an amount ofimage data.

Accordingly, even if image data has high resolution and a large amountof data, the image data may be efficiently decoded and restored by usinga size of a coding unit and an encoding mode, which are adaptivelydetermined according to characteristics of the image data, by usinginformation about an optimum encoding mode received from an encoder.

A method of determining coding units having a tree structure, aprediction unit, and a transformation unit, according to an exemplaryembodiment, will now be described with reference to FIGS. 11 through 21.

FIG. 11 is a diagram for describing a concept of hierarchical codingunits according to an exemplary embodiment.

A size of a coding unit may be expressed in width×height, and may be64×64, 32×32, 16×16, and 8×8. A coding unit of 64×64 may be split intopartitions of 64×64, 64×32, 32×64, or 32×32, and a coding unit of 32×32may be split into partitions of 32×32, 32×16, 16×32, or 16×16, a codingunit of 16×16 may be split into partitions of 16×16, 16×8, 8×16, or 8×8,and a coding unit of 8×8 may be split into partitions of 8×8, 8×4, 4×8,or 4×4.

In video data 310, a resolution is 1920×1080, a maximum size of a codingunit is 64, and a maximum depth is 2. In video data 320, a resolution is1920×1080, a maximum size of a coding unit is 64, and a maximum depth is3. In video data 330, a resolution is 352×288, a maximum size of acoding unit is 16, and a maximum depth is 1. The maximum depth shown inFIG. 11 denotes a total number of splits from a maximum coding unit to aminimum decoding unit.

If a resolution is high or a data amount is large, a maximum size of acoding unit may be large to not only increase encoding efficiency butalso to accurately reflect characteristics of an image. Accordingly, themaximum size of the coding unit of the video data 310 and 320 having thehigher resolution than the video data 330 may be 64.

Since the maximum depth of the video data 310 is 2, coding units 315 ofthe video data 310 may include a maximum coding unit having a long axissize of 64, and coding units having long axis sizes of 32 and 16 sincedepths are deepened to two layers by splitting the maximum coding unittwice. Meanwhile, since the maximum depth of the video data 330 is 1,coding units 335 of the video data 330 may include a maximum coding unithaving a long axis size of 16, and coding units having a long axis sizeof 8 since depths are deepened to one layer by splitting the maximumcoding unit once.

Since the maximum depth of the video data 320 is 3, coding units 325 ofthe video data 320 may include a maximum coding unit having a long axissize of 64, and coding units having long axis sizes of 32, 16, and 8since the depths are deepened to 3 layers by splitting the maximumcoding unit three times. As a depth deepens, detailed information may beprecisely expressed.

FIG. 12 is a block diagram of an image encoder 400 based on codingunits, according to an exemplary embodiment.

The image encoder 400 performs operations of the coding unit determiner120 of the video encoding apparatus 100 to encode image data. In otherwords, an intra predictor 410 performs intra prediction on coding unitsin an intra mode, from among a current frame 405, and a motion estimator420 and a motion compensator 425 performs inter estimation and motioncompensation on coding units in an inter mode from among the currentframe 405 by using the current frame 405, and a reference frame 495.

Data output from the intra predictor 410, the motion estimator 420, andthe motion compensator 425 is output as a quantized transformationcoefficient through a transformer 430 and a quantizer 440. The quantizedtransformation coefficient is restored as data in a spatial domainthrough an inverse quantizer 460 and an inverse transformer 470, and therestored data in the spatial domain is output as the reference frame 495after being post-processed through a deblocking unit 480 and a loopfiltering unit 490. The quantized transformation coefficient may beoutput as a bitstream 455 through an entropy encoder 450.

In order for the image encoder 400 to be applied in the video encodingapparatus 100, all elements of the image encoder 400, i.e., the intrapredictor 410, the motion estimator 420, the motion compensator 425, thetransformer 430, the quantizer 440, the entropy encoder 450, the inversequantizer 460, the inverse transformer 470, the deblocking unit 480, andthe loop filtering unit 490 perform operations based on each coding unitfrom among coding units having a tree structure while considering themaximum depth of each maximum coding unit.

Specifically, the intra predictor 410, the motion estimator 420, and themotion compensator 425 determines partitions and a prediction mode ofeach coding unit from among the coding units having a tree structurewhile considering the maximum size and the maximum depth of a currentmaximum coding unit, and the transformer 430 determines the size of thetransformation unit in each coding unit from among the coding unitshaving a tree structure.

FIG. 13 is a block diagram of an image decoder 500 based on codingunits, according to an exemplary embodiment.

A parser 510 parses encoded image data to be decoded and informationabout encoding required for decoding from a bitstream 505. The encodedimage data is output as inverse quantized data through an entropydecoder 520 and an inverse quantizer 530, and the inverse quantized datais restored to image data in a spatial domain through an inversetransformer 540.

An intra predictor 550 performs intra prediction on coding units in anintra mode with respect to the image data in the spatial domain, and amotion compensator 560 performs motion compensation on coding units inan inter mode by using a reference frame 585.

The image data in the spatial domain, which passed through the intrapredictor 550 and the motion compensator 560, may be output as arestored frame 595 after being post-processed through a deblocking unit570 and a loop filtering unit 580. Also, the image data that ispost-processed through the deblocking unit 570 and the loop filteringunit 580 may be output as the reference frame 585.

In order to decode the image data in the image data decoder 230 of thevideo decoding apparatus 200, the image decoder 500 may performoperations that are performed after the parser 510.

In order for the image decoder 500 to be applied in the video decodingapparatus 200, all elements of the image decoder 500, i.e., the parser510, the entropy decoder 520, the inverse quantizer 530, the inversetransformer 540, the intra predictor 550, the motion compensator 560,the deblocking unit 570, and the loop filtering unit 580 performoperations based on coding units having a tree structure for eachmaximum coding unit.

Specifically, the intra predictor 550 and the motion compensator 560perform operations based on partitions and a prediction mode for each ofthe coding units having a tree structure, and the inverse transformer540 perform operations based on a size of a transformation unit for eachcoding unit.

FIG. 14 is a diagram illustrating deeper coding units according todepths, and partitions, according to an exemplary embodiment.

The video encoding apparatus 100 and the video decoding apparatus 200use hierarchical coding units to consider characteristics of an image. Amaximum height, a maximum width, and a maximum depth of coding units maybe adaptively determined according to the characteristics of the image,or may be individually set according to an input of a user. Sizes ofdeeper coding units according to depths may be determined according tothe predetermined maximum size of the coding unit.

In a hierarchical structure 600 of coding units, according to anexemplary embodiment, the maximum height and the maximum width of thecoding units are each 64, and the maximum depth is 4. Since a depthdeepens along a vertical axis of the hierarchical structure 600, aheight and a width of the deeper coding unit are each split. Also, aprediction unit and partitions, which are bases for prediction encodingof each deeper coding unit, are shown along a horizontal axis of thehierarchical structure 600.

In other words, a coding unit 610 is a maximum coding unit in thehierarchical structure 600, wherein a depth is 0 and a size, i.e., aheight by width, is 64×64. The depth deepens along the vertical axis,and a coding unit 620 having a size of 32×32 and a depth of 1, a codingunit 630 having a size of 16×16 and a depth of 2, a coding unit 640having a size of 8×8 and a depth of 3, and a coding unit 650 having asize of 4×4 and a depth of 4 exist. The coding unit 650 having the sizeof 4×4 and the depth of 4 is a minimum coding unit.

The prediction unit and the partitions of a coding unit are arrangedalong the horizontal axis according to each depth. In other words, ifthe coding unit 610 having the size of 64×64 and the depth of 0 is aprediction unit, the prediction unit may be split into partitionsinclude in the encoding unit 610, i.e. a partition 610 having a size of64×64, partitions 612 having the size of 64×32, partitions 614 havingthe size of 32×64, or partitions 616 having the size of 32×32.

Similarly, a prediction unit of the coding unit 620 having the size of32×32 and the depth of 1 may be split into partitions included in thecoding unit 620, i.e. a partition 620 having a size of 32×32, partitions622 having a size of 32×16, partitions 624 having a size of 16×32, andpartitions 626 having a size of 16×16.

Similarly, a prediction unit of the coding unit 630 having the size of16×16 and the depth of 2 may be split into partitions included in thecoding unit 630, i.e., a partition having a size of 16×16 included inthe coding unit 630, partitions 632 having a size of 16×8, partitions634 having a size of 8×16, and partitions 636 having a size of 8×8.

Similarly, a prediction unit of the coding unit 640 having the size of8×8 and the depth of 3 may be split into partitions included in thecoding unit 640, i.e. a partition having a size of 8×8 included in thecoding unit 640, partitions 642 having a size of 8×4, partitions 644having a size of 4×8, and partitions 646 having a size of 4×4.

The coding unit 650 having the size of 4×4 and the depth of 4 is theminimum coding unit and a coding unit of the lowermost depth. Aprediction unit of the coding unit 650 is only assigned to a partitionhaving a size of 4×4. Also, a prediction unit of the coding unit 650 maybe split into partitions 652 having a size of 4×2, partitions 654 havinga size of 2×4, and partitions 656 having a size of 2×2.

In order to determine the at least one coded depth of the coding unitsconstituting the maximum coding unit 610, the coding unit determiner 120of the video encoding apparatus 100 performs encoding for coding unitscorresponding to each depth included in the maximum coding unit 610.

A number of deeper coding units according to depths including data inthe same range and the same size increases as the depth deepens. Forexample, four coding units corresponding to a depth of 2 are required tocover data that is included in one coding unit corresponding to a depthof 1. Accordingly, in order to compare encoding results of the same dataaccording to depths, the coding unit corresponding to the depth of 1 andfour coding units corresponding to the depth of 2 are each encoded.

In order to perform encoding for a current depth from among the depths,a least encoding error may be selected for the current depth byperforming encoding for each prediction unit in the coding unitscorresponding to the current depth, along the horizontal axis of thehierarchical structure 600. Alternatively, the minimum encoding errormay be searched for by comparing the least encoding errors according todepths, by performing encoding for each depth as the depth deepens alongthe vertical axis of the hierarchical structure 600. A depth and apartition having the minimum encoding error in the coding unit 610 maybe selected as the coded depth and a partition type of the coding unit610.

FIG. 15 is a diagram for describing a relationship between a coding unit710 and transformation units 720, according to an exemplary embodiment.

The video encoding apparatus 100 or 200 encodes or decodes an imageaccording to coding units having sizes smaller than or equal to amaximum coding unit for each maximum coding unit. Sizes oftransformation units for transformation during encoding may be selectedbased on data units that are not larger than a corresponding codingunit.

For example, in the video encoding apparatus 100 or 200, if a size ofthe coding unit 710 is 64×64, transformation may be performed by usingthe transformation units 720 having a size of 32×32.

Also, data of the coding unit 710 having the size of 64×64 may beencoded by performing the transformation on each of the transformationunits having the size of 32×32, 16×16, 8×8, and 4×4, which are smallerthan 64×64, and then a transformation unit having the least coding errormay be selected.

FIG. 16 is a diagram for describing encoding information of coding unitscorresponding to a coded depth, according to an exemplary embodiment.

The output unit 130 of the video encoding apparatus 100 may encode andtransmit information 800 about a partition type, information 810 about aprediction mode, and information 820 about a size of a transformationunit for each coding unit corresponding to a coded depth, as informationabout an encoding mode.

The information 800 indicates information about a shape of a partitionobtained by splitting a prediction unit of a current coding unit,wherein the partition is a data unit for prediction encoding the currentcoding unit. For example, a current coding unit CU_(—)0 having a size of2N×2N may be split into any one of a partition 802 having a size of2N×2N, a partition 804 having a size of 2N×N, a partition 806 having asize of N×2N, and a partition 808 having a size of N×N. Here, theinformation 800 about a partition type is set to indicate one of thepartition 804 having a size of 2N×N, the partition 806 having a size ofN×2N, and the partition 808 having a size of N×N

The information 810 indicates a prediction mode of each partition. Forexample, the information 810 may indicate a mode of prediction encodingperformed on a partition indicated by the information 800, i.e., anintra mode 812, an inter mode 814, or a skip mode 816.

The information 820 indicates a transformation unit to be based on whentransformation is performed on a current coding unit. For example, thetransformation unit may be a first intra transformation unit 822, asecond intra transformation unit 824, a first inter transformation unit826, or a second intra transformation unit 828. Also, the encodinginformation may include transformation index information about astructure of a transformation unit according.

The image data and encoding information extractor 220 of the videodecoding apparatus 200 may extract and use the information 800, 810, and820 for decoding, according to each deeper coding unit.

FIG. 17 is a diagram of deeper coding units according to depths,according to an exemplary embodiment.

Split information may be used to indicate a change of a depth. The spiltinformation indicates whether a coding unit of a current depth is splitinto coding units of a lower depth.

A prediction unit 910 for prediction encoding a coding unit 900 having adepth of 0 and a size of 2N_(—)0×2N_(—)0 may include partitions of apartition type 912 having a size of 2N_(—)0×2N_(—)0, a partition type914 having a size of 2N_(—)0×N_(—)0, a partition type 916 having a sizeof N_(—)0×2N_(—)0, and a partition type 918 having a size ofN_(—)0×N_(—)0. FIG. 9 only illustrates the partition types 912 through918 which are obtained by symmetrically splitting the prediction unit910, but a partition type is not limited thereto, and the partitions ofthe prediction unit 910 may include asymmetrical partitions, partitionshaving a predetermined shape, and partitions having a geometrical shape.

Prediction encoding is repeatedly performed on one partition having asize of 2N_(—)0×2N_(—)0, two partitions having a size of 2N_(—)0×N_(—)0,two partitions having a size of N_(—)0×2N_(—)0, and four partitionshaving a size of N_(—)0×N_(—)0, according to each partition type. Theprediction encoding in an intra mode and an inter mode may be performedon the partitions having the sizes of 2N_(—)0×2N_(—)0, N_(—)0×2N_(—)0,2N_(—)0×N_(—)0, and N_(—)0×N_(—)0. The prediction encoding in a skipmode is performed only on the partition having the size of2N_(—)0×2N_(—)0.

Errors of encoding including the prediction encoding in the partitiontypes 912 through 918 are compared, and the least encoding error isdetermined among the partition types. If an encoding error is smallestin one of the partition types 912 through 916, the prediction unit 910may not be split into a lower depth.

If the encoding error is the smallest in the partition type 918, a depthis changed from 0 to 1 to split the partition type 918 in operation 920,and encoding is repeatedly performed on coding units 930 having a depthof 2 and a size of N_(—)0×N_(—)0 to search for a minimum encoding error.

A prediction unit 940 for prediction encoding the coding unit 930 havinga depth of 1 and a size of 2N_(—)1×2N_(—)1 (=N_(—)0×N_(—)0) may includepartitions of a partition type 942 having a size of 2N_(—)1×2N_(—)1, apartition type 944 having a size of 2N_l×N_(—)1, a partition type 946having a size of N_(—)1×2N_(—)1, and a partition type 948 having a sizeof N_l×N_(—)1.

If an encoding error is the smallest in the partition type 948, a depthis changed from 1 to 2 to split the partition type 948 in operation 950,and encoding is repeatedly performed on coding units 960, which have adepth of 2 and a size of N_(—)2×N_(—)2 to search for a minimum encodingerror.

When a maximum depth is d, split operation according to each depth maybe performed up to when a depth becomes d−1, and split information maybe encoded as up to when a depth is one of 0 to d−2. In other words,when encoding is performed up to when the depth is d−1 after a codingunit corresponding to a depth of d−2 is split in operation 970, aprediction unit 990 for prediction encoding a coding unit 980 having adepth of d−1 and a size of 2N_(d−1)×2N_(d−1) may include partitions of apartition type 992 having a size of 2N_(d−1)×2N_(d−1), a partition type994 having a size of 2N_(d−1)×N_(d−1), a partition type 996 having asize of N_(d−1)×2N_(d−1), and a partition type 998 having a size ofN_(d−1)×N_(d−1).

Prediction encoding may be repeatedly performed on one partition havinga size of 2N_(d−1)×2N_(d−1), two partitions having a size of2N_(d−1)×N_(d−1), two partitions having a size of N_(d−1)×2N_(d−1), fourpartitions having a size of N_(d−1)×N_(d−1) from among the partitiontypes 992 through 998 to search for a partition type having a minimumencoding error.

Even when the partition type 998 has the minimum encoding error, since amaximum depth is d, a coding unit CU_(d−1) having a depth of d−1 is nolonger split to a lower depth, and a coded depth for the coding unitsconstituting a current maximum coding unit 900 is determined to be d−1and a partition type of the current maximum coding unit 900 may bedetermined to be N_(d−1)×N_(d−1). Also, since the maximum depth is d anda minimum coding unit 980 having a lowermost depth of d−1 is no longersplit to a lower depth, split information for the minimum coding unit980 is not set.

A data unit 999 may be a ‘minimum unit’ for the current maximum codingunit. A minimum unit according to an exemplary embodiment may be arectangular data unit obtained by splitting a minimum coding unit 980 by4. By performing the encoding repeatedly, the video encoding apparatus100 may select a depth having the least encoding error by comparingencoding errors according to depths of the coding unit 900 to determinea coded depth, and set a corresponding partition type and a predictionmode as an encoding mode of the coded depth.

As such, the minimum encoding errors according to depths are compared inall of the depths of 1 through d, and a depth having the least encodingerror may be determined as a coded depth. The coded depth, the partitiontype of the prediction unit, and the prediction mode may be encoded andtransmitted as information about an encoding mode. Also, since a codingunit is split from a depth of 0 to a coded depth, only split informationof the coded depth is set to 0, and split information of depthsexcluding the coded depth is set to 1.

The image data and encoding information extractor 220 of the videodecoding apparatus 200 may extract and use the information about thecoded depth and the prediction unit of the coding unit 900 to decode thepartition 912. The video decoding apparatus 200 may determine a depth,in which split information is 0, as a coded depth by using splitinformation according to depths, and use information about an encodingmode of the corresponding depth for decoding.

FIGS. 18, 19, and 20 are diagrams for describing a relationship betweencoding units 1010, prediction units 1060, and transformation units 1070,according to an exemplary embodiment.

The coding units 1010 are coding units having a tree structure,corresponding to coded depths determined by the video encoding apparatus100, in a maximum coding unit. The prediction units 1060 are partitionsof prediction units of each of the coding units 1010, and thetransformation units 1070 are transformation units of each of the codingunits 1010.

When a depth of a maximum coding unit is 0 in the coding units 1010,depths of coding units 1012 and 1054 are 1, depths of coding units 1014,1016, 1018, 1028, 1050, and 1052 are 2, depths of coding units 1020,1022, 1024, 1026, 1030, 1032, and 1048 are 3, and depths of coding units1040, 1042, 1044, and 1046 are 4.

In the prediction units 1060, some encoding units 1014, 1016, 1022,1032, 1048, 1050, 1052, and 1054 are obtained by splitting the codingunits in the encoding units 1010. In other words, partition types in thecoding units 1014, 1022, 1050, and 1054 have a size of 2N×N, partitiontypes in the coding units 1016, 1048, and 1052 have a size of N×2N, anda partition type of the coding unit 1032 has a size of N×N. Predictionunits and partitions of the coding units 1010 are smaller than or equalto each coding unit.

Transformation or inverse transformation is performed on image data ofthe coding unit 1052 in the transformation units 1070 in a data unitthat is smaller than the coding unit 1052. Also, the coding units 1014,1016, 1022, 1032, 1048, 1050, and 1052 in the transformation units 1070are different from those in the prediction units 1060 in terms of sizesand shapes. In other words, the video encoding and decoding apparatuses100 and 200 may perform intra prediction, motion estimation, motioncompensation, transformation, and inverse transformation individually ona data unit in the same coding unit.

Accordingly, encoding is recursively performed on each of coding unitshaving a hierarchical structure in each region of a maximum coding unitto determine an optimum coding unit, and thus coding units having arecursive tree structure may be obtained. Encoding information mayinclude split information about a coding unit, information about apartition type, information about a prediction mode, and informationabout a size of a transformation unit. Table 1 shows the encodinginformation that may be set by the video encoding and decodingapparatuses 100 and 200.

TABLE 1 Split Information 0 (Encoding on Coding Unit having Size of 2N ×2N and Current Depth of d) Size of Transformation Unit Split SplitPartition Type Information 0 Information 1 Symmetrical Asymmetrical ofof Prediction Partition Partition Transformation Transformation SplitMode Type Type Unit Unit Information 1 Intra 2N × 2N 2N × nU 2N × 2N N ×N Repeatedly Inter 2N × N 2N × nD (Symmetrical Encode Skip N × 2N nL ×2N Type) Coding Units (Only N × N nR × 2N N/2 × N/2 having 2N × 2N)(Asymmetrical Lower Depth Type) of d + 1

The output unit 130 of the video encoding apparatus 100 may output theencoding information about the coding units having a tree structure, andthe image data and encoding information extractor 220 of the videodecoding apparatus 200 may extract the encoding information about thecoding units having a tree structure from a received bitstream.

Split information indicates whether a current coding unit is split intocoding units of a lower depth. If split information of a current depth dis 0, a depth, in which a current coding unit is no longer split into alower depth, is a coded depth, and thus information about a partitiontype, prediction mode, and a size of a transformation unit may bedefined for the coded depth. If the current coding unit is further splitaccording to the split information, encoding is independently performedon four split coding units of a lower depth.

A prediction mode may be one of an intra mode, an inter mode, and a skipmode. The intra mode and the inter mode may be defined in all partitiontypes, and the skip mode is defined only in a partition type having asize of 2N×2N.

The information about the partition type may indicate symmetricalpartition types having sizes of 2N×2N, 2N×N, N×2N, and N×N, which areobtained by symmetrically splitting a height or a width of a predictionunit, and asymmetrical partition types having sizes of 2N×nU, 2N×nD,nL×2N, and nR×2N, which are obtained by asymmetrically splitting theheight or width of the prediction unit. The asymmetrical partition typeshaving the sizes of 2N×nU and 2N×nD may be respectively obtained bysplitting the height of the prediction unit in 1:3 and 3:1, and theasymmetrical partition types having the sizes of nL×2N and nR×2N may berespectively obtained by splitting the width of the prediction unit in1:3 and 3:1

The size of the transformation unit may be set to be two types in theintra mode and two types in the inter mode. In other words, if splitinformation of the transformation unit is 0, the size of thetransformation unit may be 2N×2N, which is the size of the currentcoding unit. If split information of the transformation unit is 1, thetransformation units may be obtained by splitting the current codingunit. Also, if a partition type of the current coding unit having thesize of 2N×2N is a symmetrical partition type, a size of atransformation unit may be N×N, and if the partition type of the currentcoding unit is an asymmetrical partition type, the size of thetransformation unit may be N/2×N/2.

The encoding information about coding units having a tree structure mayinclude at least one of a coding unit corresponding to a coded depth, aprediction unit, and a minimum unit. The coding unit corresponding tothe coded depth may include at least one of a prediction unit and aminimum unit containing the same encoding information.

Accordingly, it is determined whether adjacent data units are includedin the same coding unit corresponding to the coded depth by comparingencoding information of the adjacent data units. Also, a correspondingcoding unit corresponding to a coded depth is determined by usingencoding information of a data unit, and thus a distribution of codeddepths in a maximum coding unit may be determined.

Accordingly, if a current coding unit is predicted based on encodinginformation of adjacent data units, encoding information of data unitsin deeper coding units adjacent to the current coding unit may bedirectly referred to and used.

Alternatively, if a current coding unit is predicted based on encodinginformation of adjacent data units, data units adjacent to the currentcoding unit are searched using encoded information of the data units,and the searched adjacent coding units may be referred for predictingthe current coding unit.

FIG. 21 is a diagram for describing a relationship between a codingunit, a prediction unit or a partition, and a transformation unit,according to encoding mode information of Table 1.

A maximum coding unit 1300 includes coding units 1302, 1304, 1306, 1312,1314, 1316, and 1318 of coded depths. Here, since the coding unit 1318is a coding unit of a coded depth, split information may be set to 0.Information about a partition type of the coding unit 1318 having a sizeof 2N×2N may be set to be one of a partition type 1322 having a size of2N×2N, a partition type 1324 having a size of 2N×N, a partition type1326 having a size of N×2N, a partition type 1328 having a size of N×N,a partition type 1332 having a size of 2N×nU, a partition type 1334having a size of 2N×nD, a partition type 1336 having a size of nL×2N,and a partition type 1338 having a size of nR×2N.

Split information (TU size flag) of a transformation unit is a type of atransformation index, and a current size of a transformation unit may bedetermined based on the transformation index and a prediction unit typeor a partition type of a current coding unit.

For example, when the partition type is set to be symmetrical, i.e. thepartition type 1322, 1324, 1326, or 1328, a transformation unit 1342having a size of 2N×2N is set if a TU size flag is 0, and atransformation unit 1344 having a size of N×N is set if a TU size flagis 1.

On the other hand, when the partition type is set to be asymmetrical,i.e., the partition type 1332, 1334, 1336, or 1338, a transformationunit 1352 having a size of 2N×2N is set if a TU size flag is 0, and atransformation unit 1354 having a size of N/2×N/2 is set if a TU sizeflag is 1.

Accordingly, the size of a transformation unit corresponding to thetransformation index may vary according to a prediction unit type or apartition type of a coding unit.

Referring to FIG. 21, the TU size flag is a flag having a value or 0 or1, but the TU size flag is not limited to 1 bit, and a transformationunit may be hierarchically split having a tree structure while the TUsize flag increases from 0.

In this case, the size of a transformation unit that has been actuallyused may be expressed by using a TU size flag of a transformation unit,according to an exemplary embodiment, together with a maximum size andminimum size of the transformation unit. According to an exemplaryembodiment, the video encoding apparatus 100 is capable of encodingmaximum transformation unit size information, minimum transformationunit size information, and a maximum TU size flag. The result ofencoding the maximum transformation unit size information, the minimumtransformation unit size information, and the maximum TU size flag maybe inserted into an SPS. According to an exemplary embodiment, the videodecoding apparatus 200 may decode video by using the maximumtransformation unit size information, the minimum transformation unitsize information, and the maximum TU size flag.

For example, if the size of a current coding unit is 64×64 and a maximumtransformation unit size is 32×32, then the size of a transformationunit may be 32×32 when a TU size flag is 0, may be 16×16 when the TUsize flag is 1, and may be 8×8 when the TU size flag is 2.

As another example, if the size of the current coding unit is 32×32 anda minimum transformation unit size is 32×32, then the size of thetransformation unit may be 32×32 when the TU size flag is 0. Here, theTU size flag cannot be set to a value other than 0, since the size ofthe transformation unit cannot be less than 32×32.

As another example, if the size of the current coding unit is 64×64 anda maximum TU size flag is 1, then the TU size flag may be 0 or 1. Here,the TU size flag cannot be set to a value other than 0 or 1.

Thus, if it is defined that the maximum TU size flag is‘MaxTransformSizeIndex’, a minimum transformation unit size is‘MinTransformSize’, and a transformation unit size is ‘RootTuSize’ whenthe TU size flag is 0, then a current minimum transformation unit size‘CurrMinTuSize’ that can be determined in a current coding unit, may bedefined by Equation (1):

CurrMinTuSize=max(MinTransformSize,RootTuSize/(2̂MaxTransformSizeIndex)  Equation (1)

Compared to the current minimum transformation unit size ‘CurrMinTuSize’that can be determined in the current coding unit, a transformation unitsize ‘RootTuSize’ when the TU size flag is 0 may denote a maximumtransformation unit size that can be selected in the system. In Equation(1), ‘RootTuSize/(2̂MaxTransformSizeIndex)’ denotes a transformation unitsize when the transformation unit size ‘RootTuSize’, when the TU sizeflag is 0, is split a number of times corresponding to the maximum TUsize flag, and ‘MinTransformSize’ denotes a minimum transformation size.Thus, a smaller value from among ‘RootTuSize/(2̂MaxTransformSizeIndex)’and ‘MinTransformSize’ may be the current minimum transformation unitsize ‘CurrMinTuSize’ that can be determined in the current coding unit.

According to an exemplary embodiment, the maximum transformation unitsize RootTuSize may vary according to the type of a prediction mode.

For example, if a current prediction mode is an inter mode, then‘RootTuSize’ may be determined by using Equation (2) below. In Equation(2), ‘MaxTransformSize’ denotes a maximum transformation unit size, and‘PUSize’ denotes a current prediction unit size.

RootTuSize=min(MaxTransformSize,PUSize)  Equation (2)

That is, if the current prediction mode is the inter mode, thetransformation unit size ‘RootTuSize’ when the TU size flag is 0, may bea smaller value from among the maximum transformation unit size and thecurrent prediction unit size.

If a prediction mode of a current partition unit is an intra mode,‘RootTuSize’ may be determined by using Equation (3) below. In Equation(3), ‘PartitionSize’ denotes the size of the current partition unit.

RootTuSize=min(MaxTransformSize,PartitionSize)  Equation (3)

That is, if the current prediction mode is the intra mode, thetransformation unit size ‘RootTuSize’ when the TU size flag is 0 may bea smaller value from among the maximum transformation unit size and thesize of the current partition unit.

However, the current maximum transformation unit size ‘RootTuSize’ thatvaries according to the type of a prediction mode in a partition unit isjust an example and is not limited thereto.

According to an exemplary embodiment, the current maximum transformationunit size ‘RootTuSize’ may be equal to the size of the current codingunit. According to other exemplary embodiment, the current maximumtransformation unit size ‘RootTuSize’ may be determined base on aprediction unit type or a partition type of the current prediction unitor partition. For example, the current maximum transformation unit size‘RootTuSize’ may indicate the size of a maximum square included in thecurrent prediction unit or partition.

FIG. 22 is a flowchart illustrating a video encoding method that uses atransformation index on the basis of coding units and transformationunits having a tree structure, according to an exemplary embodiment.

In operation 1210, a current picture is split into at least one maximumcoding unit. A maximum depth that indicates the total number of possiblespits may be predetermined.

In operation 1220, a coded depth to output a final encoding resultaccording to at least one split region, which is obtained by splitting aregion of each maximum coding unit according to depths, is determined byencoding the at least one split region, and a coding unit according to atree structure is determined.

The maximum coding unit is spatially split whenever the depth deepens,and thus is split into coding units of a lower depth. Each coding unitmay be split into coding units of another lower depth by being spatiallysplit independently from adjacent coding units. Encoding is repeatedlyperformed on each coding unit according to depths.

Also, a transformation unit according to partition types having theleast encoding error is determined for each deeper coding unit. In orderto determine a coded depth having a minimum encoding error in eachmaximum coding unit, encoding errors may be measured and compared in alldeeper coding units according to depths.

In the determination of the coding unit, transformation units, being adata unit in which the coding unit is transformed, may be determined.The transformation units may be determined to be a data unit minimizingan error due to the transformation on the coding unit. Thetransformation units may be determined to have the same size within asingle coding unit. As a result of performing transformation at eachlevel according to a transformation depth within a current coding unit,transformation units based on a tree structure that form a hierarchicalstructure between transformation units on the same region according totransformation depths and are independent from transformation units onthe other region may be determined.

In operation 1230, encoded image data constituting the final encodingresult according to the coded depth is output for each maximum codingunit, with encoding information about the coded depth and an encodingmode. The information about the encoding mode may include informationthat indicates a coded depth or split information, information thatindicates a partition type of a prediction unit, information thatindicates a prediction mode, information that indicates a size of atransformation unit, and a transformation index. The encoded informationabout the encoding mode may be transmitted to a decoder with the encodedimage data.

FIG. 23 is a flowchart illustrating a video decoding method that use atransformation index on the basis of the coding units and thetransformation units having a tree structure, according to an exemplaryembodiment.

In operation 1310, a bitstream of an encoded video is received andparsed.

In operation 1320, encoded image data of a current picture assigned to amaximum coding unit, and information about a coded depth and an encodingmode according to maximum coding units are extracted from the parsedbitstream. The coded depth of each maximum coding unit is a depth havingthe least encoding error in each maximum coding unit. In encoding eachmaximum coding unit, the image data is encoded based on at least onedata unit obtained by hierarchically splitting the each maximum codingunit according to depths.

According to the information that indicates the coded depth and theencoding mode, the maximum coding unit may be split into coding unitshaving a tree structure. Each of the coding units having the treestructure is determined as a coding unit corresponding to a coded depth,and is optimally encoded as to output the least encoding error.Accordingly, encoding and decoding efficiency of an image may beimproved by decoding each piece of encoded image data in the codingunits after determining at least one coded depth according to codingunits.

According to the transformation index included in the information aboutthe encoding mode, transformation units having a tree structure within acoding unit may be determined. For example, the number of splits fromthe current coding unit to a transformation unit may be read from thetransformation index. In another embodiment, it may be determinedwhether the current coding unit is split into transformation units of alower level, and thus a structure of transformation units having a treestructure may be finally read from a bitstring that indicates whethersplitting from the uppermost transformation unit to a lowertransformation unit is performed for each region of the current codingunit.

In operation 1330, the image data of each maximum coding unit is decodedbased on the information about the coded depth and the encoding modeaccording to the maximum coding units. The decoded image data may bereproduced by a reproducing apparatus, stored in a storage medium, ortransmitted through a network.

The exemplary embodiments can be written as computer programs and can beimplemented in general-use digital computers that execute the programsusing a computer readable recording medium. Examples of the computerreadable recording medium include magnetic storage media (e.g., ROM,floppy disks, hard disks, etc.) and optical recording media (e.g.,CD-ROMs, or DVDs). Alternatively, the exemplary embodiments may beembodied as signals computer-readable transmission media, such as datasignals, for transmission over a computer network, for example theInternet.

The video encoding apparatuses or video decoding apparatuses of theexemplary embodiments may include a bus coupled to every unit of theapparatus, at least one processor connected to the bus that executescommands, and a memory connected to the bus that stores commands,received messages, and generated messages.

While this invention has been particularly shown and described withreference to exemplary embodiments thereof, it will be understood bythose of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the invention as defined by the appended claims. The exemplaryembodiments should be considered in descriptive sense only and not forpurposes of limitation. Therefore, the scope of the invention is definednot by the detailed description of the invention but by the appendedclaims, and all differences within the scope will be construed as beingincluded in the present invention.

What is claimed is:
 1. A video decoding apparatus comprising: a receiverwhich receives a bitstream of an encoded video; an extractor whichextracts from the bitstream split information indicating whether acoding unit is split and transformation index information indicatingwhether a transformation unit of a current level included in a codingunit among at least one coding unit is split; and a decoder whichdetermines the at least one coding unit by using the split information,splits the transformation unit of the current level into transformationunits of a lower level when the transformation index informationindicates a split of the transformation unit of the current level, andperforms an inverse transformation on the transformation unit of thecurrent level to generate residual data corresponding to thetransformation unit of the current level when the transformation indexinformation indicates a non-split of the transformation unit of thecurrent level.
 2. The video decoding apparatus of claim 1, wherein thetransformation unit of the current level is included in the coding unit,and a size of the transformation unit of the current level is smallerthan or equal to a size of the coding unit.
 3. The video decodingapparatus of claim 2, wherein the transformation unit of the currentlevel is obtained by halving a height and a width of the coding unit. 4.The video decoding apparatus of claim 1, wherein the coding unit is adata unit in which a picture of the encoded video is encoded and thetransformation unit of the current level is a data unit in which thedata of the coding unit is transformed.